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Marine Ecology Progress Series

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MEPS 229:291-312 (2002)  -  doi:10.3354/meps229291

A bioenergetic model for estimating the food requirements of Steller sea lions Eumetopias jubatus in Alaska, USA

Arliss J. Winship*, Andrew W. Trites, David A. S. Rosen

Department of Zoology and Marine Mammal Research Unit, Fisheries Center, Room 18, Hut B-3, 6248 Biological Sciences Road, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada

ABSTRACT: A generalized bioenergetic model was used to estimate the food requirements of Steller sea lions Eumetopias jubatus in Alaska, USA. Inputs included age- and sex-specific energy requirements by date, population size and composition, and diet composition and energy content. Error in model predictions was calculated using uncertainty in parameter values and Monte Carlo simulation methods. Our model suggests that energy requirements of individuals were generally lowest in the summer breeding season (June to August) and highest in the winter (December to February) and spring (March to May) mainly due to changes in activity budgets. Predicted relative daily food requirements were highest for young animals (12 ± 3% SD and 13 ± 3% of body mass for 1 yr old males and females respectively) and decreased with age (5 ± 1% and 6 ± 1% of body mass for 14 yr old males and 22 yr old females respectively). The mean daily food requirement of pregnant females predicted by the model was only marginally greater than the predicted mean daily food requirement of non-pregnant females of the same age. However, the model suggested that the mean daily food requirement of females nursing pups was about 70% greater than females of the same age without pups. Of the 3 sets of model parameters (diet, population, and bioenergetic), uncertainty in diet and bioenergetic parameters resulted in the largest variation in model predictions. The model provides a quantitative estimate of the Steller sea lion population¹s food requirements and also suggests directions for future research.

KEY WORDS: Bioenergetic model · Eumetopias jubatus · Food consumption · Steller sea lion · Sensitivity analysis

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